From early Middle English, its definite sense as "the globe" was expressed as the earth. Historically, earth has been written in lowercase. As with Roman Terra/Tellūs and Greek Gaia, Earth may have been a personified goddess in Germanic paganism: late Norse mythology included Jörð ('Earth'), a giantess often given as the mother of Thor. In its earliest attestation, the word eorðe was already being used to translate the many senses of Latin terra and Greek γῆ gē: the ground, its soil, dry land, the human world, the surface of the world (including the sea), and the globe itself. It has cognates in every Germanic language, and their ancestral root has been reconstructed as * erþō. The Modern English word Earth developed, via Middle English, from an Old English noun most often spelled eorðe. Humanity's current impact on Earth's climate and biosphere is unsustainable, threatening the livelihood of humans and many other forms of life, and causing widespread extinctions. Humans depend on Earth's biosphere and natural resources for their survival, but have increasingly impacted the planet's environment. Humans emerged 300,000 years ago in Africa and have spread across every continent on Earth with the exception of Antarctica. Life spread globally and has been altering Earth's atmosphere and surface, leading to the Great Oxidation Event two billion years ago. During the first billion years of Earth's history, the ocean formed and then life developed within it. Through tidal locking, the Moon always faces Earth with the same side, which causes tides, stabilizes Earth's axis, and gradually slows its rotation.Įarth, like most other bodies in the Solar System, formed 4.5 billion years ago from gas in the early Solar System. Earth is orbited by one permanent natural satellite, the Moon, which orbits Earth at 384,400 km (1.28 light seconds) and is roughly a quarter as wide as Earth. Earth's axis of rotation is tilted with respect to the perpendicular to its orbital plane around the Sun, producing seasons. Earth rotates around its own axis in slightly less than a day (in about 23 hours and 56 minutes). Earth is about eight light-minutes away from the Sun and orbits it, taking a year (about 365.25 days) to complete one revolution. Of the four rocky planets, it is the largest and most massive. It is the densest planet in the Solar System.
Differences in the amount of captured energy between geographic regions (as with the equatorial region receiving more sunlight than the polar regions) drive atmospheric and ocean currents, producing a global climate system with different climate regions, and a range of weather phenomena such as precipitation, allowing components such as nitrogen to cycle.Įarth is rounded into an ellipsoid with a circumference of about 40,000 km. This process maintains the current average surface temperature of 14.76 ☌, at which water is liquid under atmospheric pressure. The water vapor acts as a greenhouse gas and, together with other greenhouse gases in the atmosphere, particularly carbon dioxide (CO 2), creates the conditions for both liquid surface water and water vapor to persist via the capturing of energy from the Sun's light. Water vapor is widely present in the atmosphere, forming clouds that cover most of the planet. It has a composition of primarily nitrogen and oxygen. Inside Earth's crust is a liquid outer core that generates the magnetosphere, deflecting most of the destructive solar winds and cosmic radiation.Įarth has a dynamic atmosphere, which sustains Earth's surface conditions and protects it from most meteoroids and UV-light at entry. Earth's land is part of Earth's crust, consisting of several slowly moving tectonic plates, which interact to produce mountain ranges, volcanoes, and earthquakes.
Most of Earth's land is somewhat humid and covered by vegetation, while large sheets of ice at Earth's polar deserts retain more water than Earth's groundwater, lakes, rivers and atmospheric water together. The remaining 29.2% of Earth's surface is land, most of which is located in the form of continental landmasses within one hemisphere, Earth's land hemisphere. Almost all of Earth's water is contained in its global ocean, covering 70.8% of Earth's surface. This is enabled by Earth being a water world, the only one in the Solar System sustaining liquid surface water. Earth is the third planet from the Sun and the only astronomical object known to harbor life.
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